The process of autophagy, or bulk degradation of cellular proteins through an evolutionarily conserved autophagosomic-lysosomal pathway, is important in survival during nutrient stress, differentiation and development, and negative growth control. However, almost nothing is known about the role of this cellular pathway in defense against intracellular pathogens. The broad objective of this proposal is to evaluate the novel hypothesis that autophagy functions as an intracellular antiviral pathway that degrades viral particles and is antagonized by viral gene products required for disease pathogenesis. In support of this hypothesis, we have previously shown that the first identified mammalian autophagy gene, beclin 1, inhibits Sindbis virus replication and protects mice against lethal Sindbis virus encephalitis. In addition, our recent data demonstrate that the well-characterized IFN-inducible antiviral molecule, PKR, is required for herpes simplex virus (HSV)-induced autophagy and that the HSV-l-encoded neurovirulence gene product, ICP34.5, antagonizes PKR-dependent autophagy in mammalian cells and Beclin 1-dependent autophagy in yeast. Together, these findings lead us to hypothesize a role for Beclin 1-dependent autophagy in antiviral host defense and a role for ICP34.5 antagonism of Beclin 1-dependent autophagy in neurovirulence. In this proposal, there are four specific aims that investigate related sub-hypotheses, including: (1) the beclin 1 autophagy gene is required for HSV-l-induced autophagy; (2) HSV-1 ICP34.5 antagonizes autophagy in virally-infected cells through a direct interaction with the Beclin 1 autophagy protein; (3) Beclin 1-dependent autophagy functions as an antiviral host defense pathway by facilitating the degradation of intracytoplasmic viral particles and this function of Beclin 1 is antagonized by ICP34.5; and (4) HSV ICP34.5 regulates HSV-1 neurovirulence through a mechanism that involves antagonism of Beclin 1-dependent autophagy. To accomplish these aims, we will use an approach involving the combined use of host cells that are deficient in autophagy and expression of Beclin 1 protein and recombinant HSV-1 viruses that encode ICP34.5 mutant proteins that are deficient in antagonism of Beclin 1-dependent autophagy. We will use these reagents to investigate the role of Beclin 1-dependent autophagy in regulating viral replication and the role of ICP34.5 antagonism of Beclin 1-dependent autophagy in regulating viral neurovirulence. Together, these studies will provide novel insights about the role of autophagy in antiviral host defense and the role of viral evasion of autophagy in neurovirulence.